Endless belts are known to be useful for continuously transporting a material from one point to another. An endless belt is positioned around a set of rollers within a transporting mechanism, at least one of the rollers being driven to transport the belt around a transport loop. The rollers can be cantilever-supported, that is, each roller is being supported at only one end such that the endless belt can slide over the unsupported end for removal and replacement. More typically, the rollers are supported at both ends such that one end support on each of the rollers is removed when the endless belt is installed, replaced, etc.
An endless belt can be of a long, flexible strip of material in which the two ends are joined or seamed. For fabric-based belts, seaming includes stitching the two ends together. For thermoplastic material-based belts, seaming can include thermally bonding the two ends together. Other means for seaming include the use of adhesives and mechanical joints, such as zippers.
A specifically designed endless belt has been used within electrophotographic printers. The belt is made of a photoreceptive material which can electrostatically capture an image when exposed to an image-wise pattern of light at an imaging station. Once exposed, the belt is rotated adjacent to a toning station which applies toner to the belt. The toner is attracted to the electrostatic image within the belt such that the toner takes on substantially the same pattern as that created by the image-wise pattern of light (i.e., a toned image). As the belt rotates, the toned image is transferred by a transfer station to, for example, a blank sheet of paper. The belt is further rotated to a charging station which electrostatically "erases" remnants of the previously created electrostatic image. Further rotated, the belt can be charged to a potential which prepares the belt to capture a subsequent image. A complete rotation of the belt through this transport loop can be continuously and rapidly repeated (charge, expose, tone, transfer, erase, charge, . . . ).
However, a challenge is associated with the use of an endless belt, which is keeping the belt properly aligned on the set of rollers. This challenge is magnified when the material being transported must be transported to a very specific location. Because an endless belt can begin to drift or walk from one lateral position on the rollers to another when one or more of the rollers apply a force unevenly across the width of the belt, steering mechanisms have been developed.
Designed to correct or counteract the drifting of the belt, known steering mechanisms have proven to be ineffective, cost-prohibitive, space-prohibitive, or a combination thereof. One known steering approach involves bending the belt in the plane in which the belt travels. For wider and stiffer belts, this approach can be ineffective.
Another known steering approach involves moving all of the rollers. However, for transport mechanisms which involve applying nip pressure to the belt, for example by an outer pressure roller and an inner back-up roller, steering by moving the inner back-up roller complicates the ability of that mechanism to apply continuous nip pressure.
Another approach for steering involves the use of one or more flared rollers to cause higher tension on one edge of the belt. Creating higher tension on one edge can cause the other edge to be unsupported or less supported which is not practical in particular processes, including certain printing processes. In addition, this approach can result in damage to the belt.
Another approach for maintaining the position of the belt involves rollers having end flanges or other end structures which can contact the edges of the belt. However, this approach can damage the edges of particularly susceptible belts.
Another known steering approach involves actively correcting the position of the belt on the rollers. Active correction systems include sensors, actuators, and control systems that can add to the cost and the space requirement of the steering architecture.
There is a need for a steering approach which is cost-effective and space-effective. In addition, that steering approach should work without the need for end flanges or flared rollers. Furthermore, that steering approach should be work even if a portion of the belt is nipped between two rollers.